| Based on the conventional dry rendering,the influence of pork phospholipids on the volatile compounds of lard,especially its key odorants,was studied,and the better extraction parameters of phospholipids from dregs of pig subcutaneous adipose fat,a lard by-product,were finally obtained,which could promote the regulation of lard odorants and the comprehensive utilization of the by-product.The main contents and results of the paper are as follows:(1)The triglyceride and phospholipids samples were extracted by solvent methods,while two other lard samples were prepared from the pig subcutaneous adipose tissue and partly de-phospholipids one via the conventional dry rendering,respectively.Two kinds of lard samples extracted by solvent,with and without the addition of phospholipids,were also heated under the same conditions for simulation.And the phospholipids contents of these samples were determined by the molybdenum blue colorimetry.The results showed that ethanol could effectively remove part of phospholipids from pig subcutaneous adipose tissue,and that in the CL-PL sample was reduced by about 1/2;in addition,the phospholipids content in the SL sample was lower(0.23 mg/g),which could well simulate the the conventional dry-rendered lard.(2)The volatiles in four kinds of lards with different treatments and in pork phospholipids were extracted and identified via SPME-GC-MS.Their peroxide values(PVs)and 2-thiobarbituric acid(TBA)values were also determined.The results showed that a large amount of lipid-derived volatiles(aldehydes,ketones,etc)and some Maillard reaction products were determined when phospholipids were heated alone.However,it in turn inhibited the lipid oxidation of lard,and promoted the Maillard reaction in lard.The amount of Maillard reaction products(such as 2,5-dimethyl pyrazine)was higher in the lard samples with higher content of phospholipids(CL,SL + PL),while their PVs and TBA values were at lower levels;expect for(E,E)-2,4-decadienal,their contents of lipid-derived products,especially hexanal and 2-pentylfuran as the indicatiors of lipid oxidation and undesirable odor,were also significantly decreased,while the control lard samples(SL,CL-PL)with lower phospholipid content were on the contrary.These results indicated that pork phospholipids served as an antioxidant in lard,which could enhance the deep-fat frying and roasted notes of lard,and improve its off-odors.(3)The characteristics of lard odorants were evaluated by quantitative description analysis(QDA).The results showed that the lard samples with higher phospholipid content(CL,SL + PL)had higher scores of deep-fat frying and roasted attributes,while that with lower phospholipid content(SL,CL-PL)had higher scores of fatty aroma,indicating that phospholipids-treatment could enhance the deep-fat frying and roasted attributes of lard,and improve its excessive fatty note,which were generally consistent with the GC-MS analysis results of volatiles in lard.(4)The correlation among key volatile compounds,lipid oxidation indexes(PV & TBA values)and sensory attributes in lard was evaluated by principal component analysis(PCA).The results showed that lard(CL,SL + PL)with high phospholipids content were correlated with the most of lard characteristic flavor,Maillard reaction products and lipid oxidation products,such as(E,E)-2,4-decadienal,(E,Z)-2,4-decadienal.While lard(SL,CL-PL)with low phospholipids content were correlated with lipid oxidation products with fatty note,PV and TBA value.Meanwhile,SL and CL-PL samples were only correlated with the fatty attribute.The result of PCA were generally consistent with that of the determination of GC-MS,PV,TBA values and QDA.(5)Comparisons between the two different methods of phospholipids extraction(acetone-ethanol method and ethanol direct extraction method)from dregs of pig subcutaneous adipose fat were done.The acetone-ethanol method was further optimized for the de-oiled times with acetone and the temperature of ethanol extration.The results showed that the direct extraction method of phospholipids with ethanol seems unsuitable for the extraction of phospholipids from the dregs with high content of oil.In addition,temperature had a powerful influence on the deoiling effect of dergs,and lard was almost insoluble in acetone at lower temperature;after increasing the deoiling temperature,it was found that the good deoiling effect of acetone with deoiling three times at room temperature can be achieved.Meanwhile,temperature also had a great influence on the extraction of phospholipids from the de-oiled dregs,and the purity of phospholipids in the dregs was the hightest at 40 ℃,which could reach 70.72 %in this study.Finally,the better extraction method of phospholipids from the dregs was acetone-ethanol method with the deoiling treatment three times and the ethanol extraction at 40 ℃.The corresponding yield(%),extraction(%),purity(%)and recovery(%)of phospholipids were 0.56 %,53.83 %,70.72 %and 38.09 %,respectively. |
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